1. Field of the Invention
This disclosure relates generally to the field of lasers, and in particular to an assembly for slab geometry semiconductor lasers and a housing which allows close-coupling of many such semiconductor lasers to pump solid-state laser gain materials.
2. Description of Related Art
Arc lamps and flash lamps are commonly used as sources to excite or stimulate solid-state laser gain media. Such sources are typically positioned parallel to an elongated crystalline structure doped with a rare earth element such as neodymium (Nd) and/or other elements. The radiation emitted by the sources are partially absorbed by the solid-state laser gain medium, thereby stimulating the solid-state laser gain medium, and re-emitting radiation at a wavelength characteristic of the solid-state laser gain medium.
Such arc lamps or flash lamps in the prior art have known disadvantages as pump sources. For example, such lamps may generate a very broad radiation spectrum, but typically only a small fraction of the radiation spectrum is absorbed by the solid-state laser gain medium. In the prior art, broadband-emitting lamps for lasers, such as arc lamps and flash lamps, typically pump the entire solid-state laser gain medium of the solid-state laser indiscriminately, and thus much of the pump energy is directed to regions of the solid-state laser gain medium outside the region in which the Transverse Electromagnetic mode (TEM mode), such as TEM00, is occupying. Hence, much of the pump energy is not contributing to amplification of a single mode oscillation, but instead to various TEMs or multi-mode outputs.
Some relatively high efficiencies have been attained in high power semiconductor lasers fabricated from GaAs and GaAlAs materials by various methods known in the art, such as molecular beam epitaxy (MBE) and metallorganic chemical vapor deposition (MOCVD). Such fabricated semiconductor lasers have been used as relatively reliable pump sources for pumping the solid-state laser gain medium. One significant advantage of such semiconductor lasers is the ability to fabricate such lasers to emit radiation at specific wavelengths which match absorption values or bands of the solid-state laser gain medium used in the semiconductor laser.
Another significant advantage is the relatively good electrical-power-to-optical-radiation conversion efficiency associated with using such semiconductor lasers as pump sources. Conversion efficiencies greater than 50% have been attained in the prior art.
However, one known disadvantage of such semiconductor lasers is the relatively high degree of the divergence angle of the radiation emitted from the active region of the semiconductor laser. Typically, the angle of emission perpendicular to the active region is on the order of 40.degree. at full width half maximum (FWHM), and the angle of emission parallel to the active region is on the order of 10.degree. at FWHM. Such high divergence may be compensated using lenses, such as cylindrical micro-lenses developed at Lawrence Livermore National Laboratories. Lenses for use in lasers are described, for example, in U.S. Pat. Nos. 5,080,706; 5,081,639; 5,155,631; and 5,181,224. Various lens configurations may be used to collimate a laser beam from a semiconductor laser to improve the efficiency and performance of the semiconductor laser; for example, to collectively pump regions of the solid-state laser gain medium which more closely match the region of a TEM00 mode.
Accordingly, a need exists for a lens configuration for improving the performance of semiconductor lasers.
In the prior art, semiconductor laser bar arrays are positioned and oriented to be parallel to the solid-state laser gain medium when using a "side pumping" configuration, such as described, for example, in U.S. Pat. Nos. 5,455,838; 5,485,482; and 5,572,541. However, such side pumping configurations and designs are unable to achieve high power pumping power densities, on the order of about 100 W/cm. to about 200 W/cm. Accordingly, the solid-state laser gain medium is unable to be pumped from one side or even two sides thereof.
In order to increase the pumping power density, a multitude of laser bar arrays must be used, for example, by placing many laser bar arrays in numerous positions surrounding the solid-state laser gain medium. For example, configurations of numerous laser bar arrays having a three-fold, a five-fold, and even a seven-fold symmetry have been used. However, such multi-symmetric configurations are typically more complicated and cumbersome to implement, to maintain and repair, and to operate. Accordingly, such multi-symmetric configurations in the prior art have not been practical to implement, for example, to provide required power performance with acceptable costs of implementation.
Accordingly, a need exists for semiconductor lasers configured to provide improved performance with more practical implementations.